refactor: update milestone/task status enums to new state machine values

Milestone: open/freeze/undergoing/completed/closed (was open/pending/deferred/progressing/closed)
Task: open/pending/undergoing/completed/closed (was open/pending/progressing/closed)

- Add MilestoneStatusEnum to schemas with typed validation
- Add started_at field to Milestone model
- Update all router/CLI references from progressing->undergoing
- Add completed status handling in task transition logic

cli.py

@@ -16,7 +16,9 @@ TOKEN = os.environ.get("HARBORFORGE_TOKEN", "")
 STATUS_ICON = {
     "open": "🟢",
     "pending": "🟡",
-    "progressing": "🔵",
+    "freeze": "🧊",
+    "undergoing": "🔵",
+    "completed": "✅",
     "closed": "⚫",
 }
 TYPE_ICON = {
@@ -241,7 +243,7 @@ def main():
     p_tasks = sub.add_parser("tasks", aliases=["issues"], help="List tasks")
     p_tasks.add_argument("--project", "-p", type=int)
     p_tasks.add_argument("--type", "-t", choices=["task", "story", "test", "resolution", "issue", "maintenance", "research", "review"])
-    p_tasks.add_argument("--status", "-s", choices=["open", "pending", "progressing", "closed"])
+    p_tasks.add_argument("--status", "-s", choices=["open", "pending", "undergoing", "completed", "closed"])
 
     p_create = sub.add_parser("create-task", aliases=["create-issue"], help="Create a task")
     p_create.add_argument("title")
@@ -268,7 +270,7 @@ def main():
 
     p_trans = sub.add_parser("transition", help="Transition task status")
     p_trans.add_argument("task_id", type=int)
-    p_trans.add_argument("status", choices=["open", "pending", "progressing", "closed"])
+    p_trans.add_argument("status", choices=["open", "pending", "undergoing", "completed", "closed"])
 
     p_stats = sub.add_parser("stats", help="Dashboard stats")
     p_stats.add_argument("--project", "-p", type=int)